Circular economy methods of preparing unsaturated compounds

ABSTRACT

Methods of preparing unsaturated compounds or analogs through dehydrogenation of corresponding saturated compounds and/or hydrogenation of aromatic compounds are disclosed.

CROSS-REFERENCE TO A RELATED APPLICATION

This application claims priority to U.S. Application, Ser. No.62/351,062, filed on Jun. 16, 2016, the content of which is incorporatedherein by reference in entirety.

FIELD OF THE INVENTION

This application relates to methods of preparing unsaturated compounds,especially unsaturated carbocyclic compounds useful in the fragranceindustry, through hydrogenation of aromatic compounds or dehydrogenationof saturated compounds using sustainable, green engineering and circulareconomy methods.

BACKGROUND OF THE INVENTION

Olefins (alkenes) are versatile raw materials in organic synthesis,polymerization, and chemical processes, but they are not as widelyavailable naturally as alkanes. Given the abundance of saturatedhydrocarbon or alkanes in nature, dehydrogenation of alkanes provides asustainable production of alkenes. This approach eliminates significantamount of waste generated from alternate multi-step chemical methodsthat are used to produce these olefins.

Different dehydrogenation methods have been developed. Traditionalmethods involve use of stoichiometric amounts of halogenated reagentsand/or precious metals thus generating a lot of waste. Alternateone-step catalytic methods have been developed, but productivity andselectivity remains to be an issue especially when multipleregio-isomers can be formed in the dehydrogenation process. Especiallyin the case of higher alkanes, low selectivity and conversion oftenseverely limit the utility of dehydrogenation.

Accordingly, there remains a need for green dehydrogenation methods thatcan produce high yield and great selectivity via engineering andcatalytic methods. In one aspect, the present disclosure providesinventions aiming to meet such needs.

SUMMARY OF THE INVENTION

Many fragrance intermediates and ingredients contain unsaturatedbackbones—linear or branched chain, mono- or multi-cyclic carbonbackbones with or without functional groups. Dehydrogenation from thecorresponding saturated compounds to yield these unsaturated compoundsoften encounters low-selectivity issues, giving rise to differentregio-isomers of olefins or the aromatic counterparts. To access some ofthe unsaturated carbocyclic compounds, an alternative approach isthrough hydrogenation of the corresponding aromatic carbocycles, butcontrol of hydrogenation at the olefin stage to avoid completehydrogenation to fully saturated carbocyclic compounds remains achallenge. It has been unexpectedly discovered that various newcatalytic systems and engineering methods are efficient to tackle thischallenge.

In one aspect, the present invention provides methods of preparingunsaturated compounds, especially those comprising fragrance carbocycliccompound backbones, through dehydrogenation of corresponding saturatedcompounds, wherein said fragrance compound backbones contain one or morecarbon-carbon double bonds.

In another aspect, the present invention provides methods of preparingunsaturated compounds, especially those comprising fragrance compoundbackbones, through hydrogenation of corresponding aromatic carbocycliccompounds, wherein said fragrance compound backbones contain one or morecarbon-carbon double bonds.

In one embodiment, the present invention provides a method of preparing1,1,2,3,3-pentamethyl-4,5,6,7-tetrahydro-1H-indene (THPMI) comprisingselective hydrogenation of 1,1,2,3,3-pentamethylindane (PMI).

In a preferred embodiment, the method comprises a combination of flowhydrogenation and dehydrogenation processes.

In a particularly preferred embodiment, the present invention provides amethod of preparing THPMI comprising selective hydrogenation of PMI orselective dehydrogenation of 1,1,2,3,3-pentamethyloctahydro-1H-indene(HHPMI) in combination with continuous separation of the startingmaterials, products, or by-products.

Also within the scope of this invention is a process of preparingindomuscone comprising the steps of: (a) feeding PMI into a firstreactor having a first catalyst; (b) hydrogenating PMI in the firstreactor to obtain a hydrogenation mixture containing THPMI as thedesired product, HHPMI as a by-product, and unreacted PMI; (c) feedingthe hydrogenation mixture into a second reactor having a second catalystto oxidize THPMI to indomuscone (i.e., Cashmeran), thereby obtaining anoxidation mixture that contains indomuscone, HHPMI, and PMI; (d)separating indomuscone from HHPMI and PMI to obtain an oxidization sidestream containing HHPMI and an oxidization product stream containingindomuscone; (e) feeding the oxidation side stream into a third reactorhaving a third catalyst to dehydrogenate HHPMI to PMI to obtain adehydrogenation stream; (f) feeding the dehydrogenation stream into thefirst reactor to hydrogenate PMI to THPMI; and (g) collectingindomuscone in the oxidization product stream. The process can furthercomprise the steps of: (d1) separating PMI from the oxidization sidestream to obtain a PMI oxidization stream consisting essentially of PMI;and (d2) feeding the PMI oxidization stream into the first reactor tohydrogenating PMI to THPMI. Each of the first, second, and thirdreactors is either a batch reactor or a flow reactor. When a flowreactor is used, the catalyst contained therein is preferably afixed-bed catalyst.

Still within the scope of this invention is a process of preparing THPMIcomprising the steps of: (a) feeding PMI into a first reactor having afirst catalyst; (b) hydrogenating PMI to THPMI in the first reactor toobtain a hydrogenation mixture containing THPMI as the desired product,HHPMI as a by-product, and unreacted PMI; (c) separating HHPMI from thehydrogenation mixture in a first separation column to obtain a firsthydrogenation side stream containing HHPMI and a main hydrogenationstream containing THPMI and PMI; (d) passing the first hydrogenationside stream into a second reactor having a second catalyst; (e)dehydrogenating HHPMI in the first hydrogenation side stream to PMI inthe second reactor to obtain a dehydrogenation stream; (f) feeding thedehydrogenation stream into the first reactor; (g) separating THPMI inthe main stream from PMI in a second separation column to obtain asecond hydrogenation stream containing PMI and a hydrogenation productstream containing THPMI; (h) feeding the second hydrogenation sidestream into the first reactor; and (i) collecting THPMI in thehydrogenation product stream. Each of the first and second reactors,independently, is either a batch reactor or a flow reactor. In oneembodiment, each of the first and second reactors is a flow reactor, andeach of the first and second catalysts, having a particle size of 300microns or greater, is a fixed-bed catalyst.

In some embodiments, the hydrogenating step (b) is performed using anyof the hydrogenation methods described herein, and/or thedehydrogenating step (e) is performed using any of the dehydrogenationmethods described herein.

The term “unsaturated compound” refers to an aromatic compound or analiphatic hydrocarbon having one or more carbon-carbon double bonds(C═C). The aliphatic hydrocarbon can be a cyclic (carbocyclic) compoundor straight or branched open chain without a ring. The term“corresponding saturated compound” refers to a compound having ahydrocarbon backbone the same as the unsaturated compound but having nocarbon-carbon double bond.

The term “fixed-bed catalyst” refers a catalyst, typically in pellet orgranule form, packed in a static bed that allows a gas or liquid to passthrough.

The term “flow reactor” refers to a reactor wherein reactants arecontinuously fed into the reactor and emerge as continuous stream ofproduct.

The term “batch reactor” refers to a vessel in which reactants

Other aspects or benefits of the present invention will be reflected inthe following drawings, detailed description, and claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a process scheme for pentamethyl indane (PMI) to formtetrahydro pentamethyl indane (THPMI) using combination of selectivehydrogenation, dehydrogenation and separation in a continuous mode.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect, the present invention provides a method of preparing anunsaturated compound, comprising dehydrogenation of a correspondingsaturated compound in the presence of a catalyst system under conditionsthat effect loss of one or more molecules of hydrogen (H₂) per moleculeof the saturated compound.

In one embodiment, the conditions include one or more solvents (e.g.,acetic acid, toluene, ethyl acetate, DMSO, and DMF), an elevatedtemperature (e.g., at least 50° C., at least 100° C., 50-800° C.,100-800° C., 100-400° C., and 150-350° C.), and/or a stream of nitrogento purge liberated hydrogen. In one embodiment, the conditions includeone or more hydrogen acceptor (e.g., tertiary butyl ethylene,cyclohexene and other alkenes) to consume the liberated hydrogen.

In one embodiment, the catalyst system is selected from the groupconsisting of heterogeneous catalyst systems, homogeneous catalystsystems, bi-metallic catalyst systems, and combinations thereof.

In another embodiment, the heterogeneous catalyst system is selectedfrom Pd/C, Pd/Alumina, Pd/CG, Pt/C, Pt/Alumina, Molybdenum Oxide,Vanadium Pentoxide, Rh/Alumina, Ru/Al₂O₃, Bismuth Molybdate, andcombinations thereof.

In another embodiment, the heterogeneous catalyst system is abi-metallic catalyst system comprising a metal pair including but notlimited to Pt—Sn, Pt—Tl, Pt—Co, and Pd—Ag.

In another embodiment, the homogeneous catalyst system is selected fromsoluble transition metal salts (e.g., Pd(TFA)₂, Pd(OAc)₂) with orwithout ligands, pincer-based catalysts (see J. Am. Chem. Soc. 1997,119, 840-841, Chem. Commun., 1999, 2443-2449; Alkane Dehydrogenation. InAlkane C—H Activation by Single-Site Metal Catalysis, Pérez, P. J., Ed.Springer: New York, 2012; Vol. 38., Chapter 4; Chem. Rev. 2014, 114,12024-12087; US20150251171A1), and combinations thereof.

A pincer-based catalyst is a catalyst having a metal (typically atransitional metal such as ruthenium, rhodium, palladium, osmium,iridium, and platinum) and a pincer ligand that binds tightly to threeadjacent coplanar sites, usually on a transition metal in a meridionalconfiguration.

Exemplary pincer-based catalysts include iridium complex having thestructures described in US 2015/0251171 such as (^(iPr4)PCP)Ir(C₂H₄) and(p-OK-^(iPr4)PCP)Ir(C₃H₆), in which iPr refers to isopropyl groups, PCPis C₆H₃(CH₂PBut₂)₂-2,6), Ir refers to iridium, C₂H₄ is ethylene, andC₃H₆ is propylene. The iridium complex is either unsupported orimmobilized on a solid support including silica, γ-alumina, florisil,neutral alumina.

In another embodiment, the saturated compound comprises of straightchain or branched alkanes with or without functional groups such asaldehyde, ketone, ester, ethers or in combination thereof, eachoptionally substituted.

In another embodiment the saturated compound comprises a formulaselected from the group consisting of:

wherein:

n is 0 or an integer selected from 1 to 20; X is a lactone or ether

R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, R₁₂, R₁₃, R₁₄, R₁₅, R₁₆,R₁₇ and R₁₈ are each independently H, methyl, ethyl, C₃-C₁₀ branched,cyclic or straight chain alkyl, ketone, ester, ether, aldehyde, alcoholor vinyl group, or a combination thereof, each optionally substituted;or alternatively, two R groups on the same carbon atom together form anoxo (═O) group.

In another embodiment, the saturated carbocyclic compound comprises abackbone structure selected from the group consisting of:

wherein m is an integer from 1 to 20; each of R₁₉, R₂₀, and R₂₁,independently, is hydrogen or oxo (═O), and each open position of saidbackbone structures is optionally substituted.

In another embodiment, the saturated carbocyclic compound is selectedfrom the group consisting of:

In another embodiment, the present invention provides method ofpreparing a compound of formula I(a) or I(b), comprising flowdehydrogenation of a compound of formula II (starting material) in thepresence of a fixed-bed catalyst:

wherein each of R₂₂, R₂₃, and R₂₄, independently, is H or ═O; and

Q is CH₂, CH₂CH₂, CH(CH₃), or C(CH₃)₂, preferably, Q is CH₂CH₂ orCH(CH₃).

In another embodiment, the present invention provides a method ofpreparing a compound of formula I(a) or I(b). The method comprisesselective hydrogenation of a compound of formula III in the presence ofa catalyst:

wherein Q is CH₂, CH₂CH₂, CH(CH₃), or C(CH₃)₂.

In another embodiment, the catalyst is a fixed-bed catalyst, and thehydrogenation is conducted in a flow reactor.

In another embodiment, the hydrogenation reaction is combined withdehydrogenation reaction and continuous separation process to separateproduct from the starting material and by-product.

In another embodiment, the compound of formula (III) is1,1,2,3,3-pentamethylindane (PMI), and said formula I(a) is1,1,2,3,3-Pentamethyl-4,5,6,7-tetrahydro-1H-indene (THPMI):

In another embodiment, the present invention provides a method ofpreparing 1,1,2,3,3-pentamethylindane (PMI), comprising flowdehydrogenation of 1,1,2,3,3-pentamethyloctahydro-1H-indene (HHPMI) inthe presence of a fixed-bed catalyst:

In another embodiment, the fixed-bed catalyst comprises 5% Pd/C, and thedehydrogenation is conducted in a flow reactor, and a nitrogen stream ispassed through the reactor to remove hydrogen molecules formed.

In another embodiment, the dehydrogenation reaction is combined withselective hydrogenation of PMI to form THPMI.

In other embodiments, the present invention provides selectivedehydrogenation of a saturated carbocyclic compound to form anunsaturated carbocyclic compound as substantially described and shown.

In other embodiments, the present invention provides selectivehydrogenation of an aromatic compound to form an unsaturated carbocycliccompound as substantially described and shown.

While not intended to be limiting, the generic structures of thefragrance backbones are used to illustrate application of thetechnologies disclosed herein in synthesis of compounds useful asfragrances, and the general technology of dehydrogenation is applicableto synthesis of these backbones to introduce double bond(s) into themolecule using various precious and non-precious metal catalyst systems.

The method for dehydrogenation for these substrates can be Standarddehydrogenation using catalysts including but not limited toheterogeneous dehydrogenation catalysts: platinum group metals,combination of metals, supported and non-supported metal catalysts andhomogenous catalysts including but not limited to pincer based catalystsystems with or without hydrogen acceptor. The method fordehydrogenation can also be oxidative dehydrogenation using oxygen, air,peroxides and catalysts including but not limited to heterogeneouscatalysts such as boric acid, vanadium oxide, molybdenum oxide supportedor unsupported and homogeneous catalysts including but not limited tometal complexes with or without solvents and ligand systems. Theoperating temperatures for dehydrogenations can be from 50 to 800° C.(with a lower limit of 50, 80, 100, 120, 150, or 200° C. and an upperlimit of 800, 700, 600, 500, 400, 300, 200, or 150° C.), more preferablyin the range of 100-400° C.

The following general synthetic schemes illustrate utility of thedehydrogenation processes to the synthesis of fragrance-relatedcompounds:

Useful Intermediates for Fragrance Applications

In the above schemes,

is a single or double bond and at least one

is a double bond.

The values and dimensions disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such value is intended to mean both therecited value and a functionally equivalent range surrounding thatvalue. For example, a value disclosed as “50%” is intended to mean“about 50%.”

The invention is described in greater detail by the followingnon-limiting examples. Without further elaboration, it is believed thatone skilled in the art can, based on the description herein, utilize thepresent invention to its fullest extent. All publications cited hereinare incorporated by reference in their entirety.

Example 1: Dehydrogenation Using Commercial Heterogeneous Catalysts

Two commercially available heterogeneous catalysts 5% Pd/C and 10% Pd/Cwere used to prepare fragrance ingredients such as galaxolide analogs(e.g., Galaxolide HC, which is2,3-Dihydro-1,1,2,3,3-Pentamethyl-1H-Indene, hereinafter “PMI”) from1,1,2,3,3-pentamethyloctahydro-1H-indene (HHPMI) at 70% and 100% yieldsrespectively, as demonstrated in the following formula:

Example 2: Selective Dehydrogenation Using Bi-Metallic CatalystFormulations

Different compositions of bimetallic catalyst systems were prepared andtested for preparation of THPMI from HHPMI. (Cf the limited literatureprecedents: Pt—Sn, Pt—Tl, Pt—Co, Pd—Ag with a selectivity of 25-60% anda very low conversion (<5%). See Applied Catalysis A: General Volume 469(2014), 300-305; International Journal of hydrogen energy 37(2012),6756-63.)

Use of the 5% Pd-1% Ag catalyst on silica support led to 26% selectivityof THPMI at about 10% conversion from HHPMI.

Various combinations and compositions of bi-metallic systems could beprepared and usable in preparing an unsaturated compound includingTHPMI.

Example 3: Selective Dehydrogenation Using Homogeneous Pincer-BasedCatalyst Systems

Suitable homogenous iridium-based pincer catalyst systems include thosereported in the publications such as J. Am. Chem. Soc. 1997, 119,840-41; Chem. Commun. 1999, 2443-49; Alkane Dehydrogenation, In AlkaneC—H Activation by Single-Site Metal Catalysis, Pérez, P. J., Ed.Springer: New York, 2012, Vol. 38, Chapter 4; Chem. Rev. 2014, 114,12024-87; and US20150251171A1.

Dehydrogenation using homogeneous pincer based catalyst systems giveshigh conversions, e.g., 50% or higher, with high selectivity (e.g., 80%or high and 90% or higher) for unsaturated backbones described above andthose shown below:

Example 4: Oxidative Dehydrogenation

Oxidative dehydrogenation of cycloalkane to cycloalkene using boric acidinvolves a 2-step process, oxidation to alcohol and dehydration tocycloalkene.

Suitable catalysts include molybdenum oxide, vanadium oxide,magnesium-doped vanadium and molybdenum oxide, and cobalt-doped vanadiumphosphorous oxide with or without various oxidants using one stepprocess. Other useful catalysts are described in J. Cat. 12, 287-91(1991); J. Cat. 164, 28-35 (1996); Journal of the Taiwan Institute ofChemical Engineers (2015) 1-10). As an illustration, oxidativedehydrogenation of cyclohexane to cyclohexene was achieved in 70%selectivity at 40% conversion.

Results from Cyclopentadecane dehydrogenation are shown in Table 1below:

TABLE 1 Conditions Catalyst In a batch reactor at Molybdenum Oxide 180°C. 800 rpm With Air In a flow reactor at Vanadium Oxide 450° C. Pd/CG NoAir

Example 5

Results on Isolongifolene dehydrogenation using various catalyst systemsare shown below:

Example 6

Dehydrogenation of ketones or aldehydes can yield the correspondingα,β-unsaturated ketones or aldehydes using the catalysts described aboveincluding palladium catalysts, e.g., palladium (II) acetate Pd(OAc)₂ anddimethyl sulfoxide (DMSO) coordinated palladium trifluoroacetatePd(DMSO)₂(TFA)₂ with oxygen and solvent. See, e.g., S. Stahl et al,Chem. Sci., 2012, 3, 887-891; J. Zhu et al., Adv. Synth. Catal., 2009,351, 1229; J. Liu et al., Chem.-Asian J., 2009, 4, 1712; and Zhao et al,Chem. Sci., 2012, 3, 883-886.

In the scheme above, the reaction is carried out using DMSO coordinatedpalladium (II) trifluoroacetate Pd(TFA)₂ with oxygen (O₂) at a pressureof 1 atmosphere in ethyl acetate (EtOAc) at a temperature of 60 to 80°C.

Specific applications to fragrance backbones are shown below.

Example 7: Engineering Solution to Enhance Yield of Mono-UnsaturatedAlkene Via Combination of Hydrogenation, Dehydrogenation andSeparation-THPMI

The selective hydrogenation of 1,1,2,3,3-pentamethylindane (PMI) to1,1,2,3,3-pentamethyl-4,5,6,7-tetrahydro-1H-indene (THPMI) is anintermediate step in the synthesis of Cashmeran family of products. Asignificant amount of over-hydrogenated by-product is formed in knownprocesses.

A process of this invention is a breakthrough to this long standingproblem in the known processes. This process utilizes a combination ofhydrogenation and dehydrogenation steps in converting the waste streamto the starting material (PMI) and then converting PMI to THPMI in acontinuous fashion, e.g., in a flow reactor. The combination ofselective hydrogenation and dehydrogenation in flow reactors turn thewaste stream to the useful intermediates or products in a continuousreactor, e.g., a flow reactor, thus improving the overall yield.

THPMI is prepared following these steps: (a) feeding PMI into a firstflow reactor having a fixed bed catalyst; (b) hydrogenating PMI in thefirst flow reactor to produce a product mixture; (c) separating HHPMIfrom the product mixture in a first separation column to obtain a firstside stream containing the by-product HHPMI and a main stream containingTHPMI; (d) passing the first side stream into a second flow reactorhaving a second fixed bed catalyst; (e) dehydrogenating HHPMI to PMI inthe second flow reactor to obtain a dehydrogenation stream; (f) feedingthe dehydrogenation stream into the first flow reactor; (f) separatingthe main stream in a second separation column to obtain a second sidestream containing PMI and a product stream containing THPMI with apurity of 85% or greater; (g) feeding the second side stream into thefirst flow reactor; and (h) collecting the product stream containingTHPMI.

The first fixed bed catalyst provides a high selectivity for preparingTHPMI. Any catalysts described above can be used as the first fixed bedcatalyst.

This process of the invention can have a continuous 2-column separationof THPMI from the reaction mixture with a high efficiency and a highpurity, e.g., at 85% or greater, and at the same time, recovering theby-product HHPMI and the unreacted starting material PMI in a separateside stream. PMI is then fed into the first flow reactor, i.e., thehydrogenation flow reactor, to be converted to THPMI. HHPMI is fed intothe second flow reactor, i.e., the dehydrogenation reactor, to beconverted to PMI, which is in turn fed into the first flow reactor forconversion to THPMI.

This process scheme is depicted in FIG. 1 and described in greaterdetail below.

Flow Hydrogenation of PMI

PMI is allowed to pass through the first flow reactor containing thefirst fixed bed catalyst. In the first flow reactor, PMI is selectivelyhydrogenated to the desired product THPMI. The reaction is highlyexothermic and preferred carried out at a high pressure (e.g., >500 psiand 600 to 1200 psi) in the flow reactor and a temperature of 165-185°C. for good selectivity of THPMI. Major by-product obtained from thereaction is HHPMI from over hydrogenation of THPMI as shown in the sidereaction below. Some unreacted PMI is also present for typical processconditions.

Side Reaction

Catalysts for Hydrogenation

Several fixed bed catalysts were used in the hydrogenation of PMI toTHPMI. The results are shown in the Table 2 below. Combining thisprocess with continuous separation and dehydrogenation of waste streams(described in following sections) has proved to prepare THPMI in a highoverall yield. The overall yield is calculated as: the actual yield ofTHPMI by weight/the theoretical yield of THPMI based on the initial PMIfed into the flow reactor×100%.

TABLE 2 Hydrogenation results using different types of of fixed bed 5%Pd/C catalysts Avg. Gas Liquid THPMI Pressure flowrate flowrate T Conc.Conversion Selectivity Catalyst (psi) (sccm) (ml/min) (° C.) (%) PMI (%)(%) Catalyst A 700 60 0.2 180 44.6 66.7 67 Catalyst B 700 30 0.15 17518.8 50.7 37 Catalyst C 700 60 0.12 170 47.4 60.6 78 Catalyst D 700 250.17 165 43.2 59 74

Avg. Pressure is calculated as (the pressure in the inlet of the flowreactor+the pressure in the outlet of the flow reactor)/2.

The gas flow rate refers to the flow rate of hydrogen gas fed into theflow reactor measured at 1 atmosphere and 0° C. It is measured in sccmunits, i.e., Standard Cubic Centimeters per Minute, indicating cm³/minat a standard temperature and pressure (i.e., 1 atmosphere and 0° C.).The standard temperature and pressure vary according to differentregulatory bodies.

The liquid flow rate is the flow rate of PMI fed into the flow reactor.

THPMI is the concentration of THMPI in the stream coming out of the flowreactor.

Conversion PMI is the moles of PMI consumed/the moles of PMI fed intothe flow reactor.

The selectivity is calculated as the moles of THPMI/the total moles ofPMI consumed.

Continuous Separation of Product Stream Containing THPMI

The product stream from the hydrogenation contains the desired productTHPMI, the by-product HHPMI, and the unreacted PMI. THPMI is separatedfrom the product stream using two separate columns, together having ahigh efficiency of 40-50 stage separation. After the separation, THPMIis obtained at a purity of 85%. HHPMI is easily separated from THPMI andPMI using a separation column, leaving a mixture of THPMI and PMI, whichrequires a separation column with a very high efficiency.

Flow Dehydrogenation of HHPMI to PMI

The separated HHPMI constitutes about 20 to 25% of the product stream.It is then dehydrogenated to PMI in a second flow reactor. The newlygenerated PMI is allowed to pass through the first flow reactor again tobe converted to THPMI.

The reaction is an equilibrium limited process and in order to drive theprocess to the desired product, hydrogen must be removed from theprocess. Nitrogen is typically used to purge the liberated hydrogen fromthe system. The reaction is highly endothermic and requires highoperating temperatures and high catalyst loading.

Catalysts for Dehydrogenation

Catalysts suitable for dehydrogenation of HHPMI include Pd/C and Pt/C.The dehydrogenation results are shown in Table 2 below. The results show˜70% conversion of HHPMI to PMI with these two catalysts.

TABLE 3 Dehydrogenation results in the second flow reactor usingdifferent types of 5%, Pd/C Nitrogen Liquid Conv. of Catalyst flowrateflowrate T HHPMI to Entry# (sccm) (ml/min) (° C.) PMI (%) Catalyst C 100.03 340 69.12 Catalyst D 10 0.05 300 70.06

Process Scheme

Based on the results from continuous hydrogenation, distillation anddehydrogenation, a new process scheme proposed to obtain 85% THPMI yieldat low cost is illustrated in FIG. 1.

Experimental Setup for Hydrogenation of PMI

The liquid reactant was pumped using the HPLC pump which can deliverliquid in the flowrate range from 0 to 10 ml/min. The hydrogen gas flowsthrough the Mass Flow Controller (MFC) at the desired flowrate and mixedwith the liquid stream using a micromixer. The combined gas-liquidmixture then entered the fixed bed reactor which was immersed in aconstant temperature oil bath (or heated using electric furnace). Fritsmade of SS316L, with 2 microns opening were connected to the ends of thereactor to prevent the catalyst from moving out of the reactor. From thereactor, the reaction mixture was passed through the back pressureregulator. From the back pressure regulator, the mixture was passed to aproduct receiver where the liquid was collected in a glass vessel andthe gas phase is vented to the atmosphere.

Experimental Setup for Dehydrogenation of PMI

The liquid reactant is pumped using the HPLC pump which can deliverliquid in the flowrate range from 0 to 10 mL/min. Compressed nitrogenflows through the Mass Flow Controller (MFC) at the desired flow andmixed with the liquid stream using a micromixer. The combined gas-liquidmixture then enters the fixed bed reactor containing the catalyst whichis heated using an electric furnace. From the reactor, the reactionmixture is cooled using a cooling bath and then the product mixture iscollected in a receiver.

The foregoing examples or preferred embodiments are provided forillustration purpose and are not intended to limit the presentinvention. Numerous variations and combinations of the features setforth above can be utilized without departing from the present inventionas set forth in the claims.

What is claimed is:
 1. A method of preparing an unsaturated compound,comprising dehydrogenation of a corresponding saturated compound in thepresence of a catalyst system under conditions that effect loss of oneor more molecules of hydrogen (H₂) per molecule of the saturatedcompound.
 2. The method of claim 1, wherein said conditions comprise oneor more solvents, an elevated temperature, a stream of nitrogen to purgeliberated hydrogen, and any combination thereof.
 3. The method of claim1, further comprising adding one or more hydrogen acceptors to thedehydrogenation reaction to consume the hydrogen molecules.
 4. Themethod of claim 1, wherein said catalyst system is selected from thegroup consisting of heterogeneous catalyst systems, homogeneous catalystsystems, and combinations thereof.
 5. The method of claim 4, whereinsaid heterogeneous catalyst system is selected from the group consistingof Pd/C, Pd/Alumina, Pd/CG, Pt/C, Pt/Alumina, Molybdenum Oxide, VanadiumPentoxide, Rh/Alumina, Ru/Al₂O₃, Bismuth Molybdate, bi-metallic catalystsystems comprising of metal pairs, and combinations thereof.
 6. Themethod of claim 4, wherein said homogeneous catalyst system is selectedfrom soluble transition metal salts, Pincer-based catalysts, andcombinations thereof.
 7. The method of claim 1, wherein the saturatedcompound is a straight chain or branched alkane with or without one ormore functional groups, each optionally substituted.
 8. The method ofclaim 1, wherein said saturated compound is a compound of a formulaselected from the group consisting of:

wherein: n is 0 or an integer selected from 1 to 20; X is a lactone orether; and R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, R₁₂, R₁₃, R₁₄,R₁₅, R₁₆, R₁₇, and R₁₈ are each independently H, methyl, ethyl, C₃-C₁₀branched or straight chain alkyl, ketone, ester, ether, or vinyl group,or a combination thereof, each optionally substituted; or alternatively,two R groups on the same carbon atom together form an oxo (═O) group. 9.The method of claim 1, wherein said saturated compound comprises abackbone structure selected from the group consisting of:

wherein m is an integer from 1 to 20; R is hydrogen or oxo (═O), andeach open position of said backbone structures is optionallysubstituted.
 10. The method of claim 1, wherein said saturated compoundis selected from the group consisting of:


11. The method of claim 1, wherein the unsaturated compound is acompound of formula I(a) or I(b), and the saturated compound is acompound of formula II:

wherein R is H or ═O; and Q is CH₂, CH₂CH₂, CH(CH₃), or C(CH₃)₂.
 12. Themethod of claim 1, wherein the unsaturated compound is1,1,2,3,3-pentamethylindane (PMI), the saturated compound is1,1,2,3,3-pentamethyloctahydro-1H-indene (HHPMI), and thedehydrogenation is performed in a flow reactor in the presence of afixed-bed catalyst:


13. The method of claim 12, wherein said fixed-bed catalyst comprises 5%Pd/C, a nitrogen stream is passed through the flower reactor to removehydrogen molecules formed, and the dehydrogenation reaction is combinedwith selective hydrogenation of PMI to form THPMI.
 14. A method ofpreparing a compound of formula I(a) or I(b), comprising selectivehydrogenation of a compound of formula III in the presence of acatalyst:

wherein Q is CH₂, CH₂CH₂, CH(CH₃), or C(CH₃)₂.
 15. The method of claim14, wherein said catalyst is a fixed-bed catalyst, and the hydrogenationis conducted in a flow reactor.
 16. The method of claim 14, wherein thehydrogenation reaction is combined with dehydrogenation reaction and acontinuous separation process to separate product from the startingmaterial.
 17. The method of claim 14, wherein said compound of formula(III) is 1,1,2,3,3-pentamethylindane (PMI), and said formula I(a) is1,1,2,3,3-Pentamethyl-4,5,6,7-tetrahydro-1H-indene (THPMI):


18. A process of preparing1,1,2,3,3-Pentamethyl-4,5,6,7-tetrahydro-1H-indene (THPMI) comprisingthe steps of: (a) feeding 1,1,2,3,3-pentamethylindane (PMI) into a firstreactor having a first catalyst; (b) hydrogenating PMI in the firstreactor to obtain a hydrogenation mixture containing THPMI as thedesired product, 1,1,2,3,3-pentamethyloctahydro-1H-indene (HHPMI) as aby-product, and optionally unreacted PMI; (c) separating HHPMI from thehydrogenation mixture in a first separation column to obtain a firstside stream containing HHPMI and a main stream containing THPMI and PMI;(d) passing the first side stream into a second flow reactor having asecond catalyst; (e) dehydrogenating HHPMI to PMI in the second flowreactor to obtain a dehydrogenation stream; (f) feeding thedehydrogenation stream into the first flow reactor; (g) separating THPMIin the main stream from PMI in a second separation column to obtain asecond side stream containing PMI and a product stream containing THPMI;(h) feeding the second side stream into the first flow reactor; and (i)collecting the product stream containing THPMI.
 19. The process of claim18, wherein each of the first and second reactors, independently, is abatch reactor or a flow reactor.
 20. The process of claim 19, whereineach of the first and second reactors is a flow reactor, and each of thefirst and second catalysts, having a particle size of 300 microns orgreater, is independently a fixed-bed catalyst.